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    <title>ShellCheck: SC2300 – Parameter expansion can't be applied to command substitutions. Use temporary variables.</title>
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    <h1>SC2300 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2300">See this page on GitHub</a>
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    <h2
id="parameter-expansion-cant-be-applied-to-command-substitutions-use-temporary-variables">Parameter
expansion can't be applied to command substitutions. Use temporary
variables.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2300.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;Building </span><span class="va">${$</span><span class="er">(git rev-parse --show-toplevel)##*/</span><span class="va">}</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2300.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="va">tmp</span><span class="op">=</span><span class="va">$(</span><span class="fu">git</span> rev-parse <span class="at">--show-toplevel</span><span class="va">)</span></span>
<span id="cb2-2"><a href="SC2300.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;Building </span><span class="va">${tmp</span><span class="op">##</span><span class="pp">*</span>/<span class="va">}</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>ShellCheck found a parameter expansion that begins with a command
substitution, such as <code>$(..)</code> or <code>`..`</code>. This is
not valid. Parameter expansion only works on variables (normal or
special).</p>
<p>In the example, the user hoped to apply the construct
<code>${var##*/}</code>, stripping the path, to the current git root
directory as output by <code>git rev-parse --show-toplevel</code>. Since
parameter expansion only works on variable, the command substitution
must be assigned to a variable first like in the correct example.</p>
<p>If the goal was instead to dynamically generate a variable name to
expand, see <a href="SC2082.html">SC2082</a>.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>None</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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